The present invention relates to a device for illuminating a display unit such as a liquid crystal display (LCD) unit used to display exposure data or the like in the viewfinder of a camera.
Heretofore, exposure data and the like has been displayed with a mechanical meter, a light-emitting diode (LED) display unit or an LCD unit in the viewfinder of a camera. In the case where a mechanical meter is employed, the mechanical meter must be sufficiently small in size that it can be built into the camera, and it should be so designed that the needle is deflected by small current. Such a mechanical meter can relatively easily be broken by physical impact or damaged by vibration. An LED unit is free from such a drawback because it, unlike the mechanical meter, has no movable parts. However, the LED is disadvantageous in that the electric power consumption thereof is relatively large.
In order to eliminate the above-described drawbacks accompanying mechanical meters and LED display units, recently, a display system using a liquid crystal display (LCD) unit has been proposed. An LCD unit, like an LED, has no movable components. Therefore, the LCD unit cannot easily be damaged by mechanical impact. Moreover, it has a lower power consumption compared with an LED unit. However, in the case where a photographing operation is carried out at a dark place, it is rather difficult to read the display effected by the LCD unit, and therefore it is necessary to provide an illuminating device for the LCD unit.
A conventional illuminating device for illuminating an LCD unit is designed so that an operating switch is turned on to activate a light source (lamp), and the light source is turned off immediately when the operating switch is turned off. However, this device is disadvantageous in that, since the photographer must adjust the aperture value and the shutter speed while referring to the exposure data displayed in the view finder, in a photographing operation at a dark place, he must adjust the camera while depressing the operating switch. This is considerably troublesome. In order to eliminate this difficulty, a method has been proposed in which the illuminating device is provided with a timer which starts when the operating switch has been released. However, that method is still disadvantageous in that it is difficult to establish an illumination time period adequate for all situations, and also electric power may be wasted because the light source is liable to be kept turned on after the photographing operation has been completed.